JPH03105293A - Emergency core cooling system - Google Patents

Abstract

PURPOSE:To lower pool surface temperature and to reduce the inner pressure of a nuclear reactor containment vessel at a loss of coolant accident LOCA by providing a coolant return pipe connecting a pressure vessel to a suppression pool, and by supplying a coolant in the suppression pool, to the pressure vessel. CONSTITUTION:At a LOCA, steam discharged to a drywell 2 from a pressure vessel 1, is introduced to a suppression pool 4 through a vent tube to be condensed there and the water level in a pressure suppression chamber 3 rises. On the other hand, from the relation-ship between free water levels in the pressure vessel 1 and the vent tube 5, influenced by the release of an automatic pressure reducing valve 6, a coolant increment in the pressure suppression chamber 3 is injected into the pressure vessel 1 by gravity force. In this occasion, high temperature water which is brought in from a water intake 10 placed at the upper part of the suppression pool 4, passes through the low temperatured bottom part of the pool via a return pipe 8, and therefore water temperature at the pool bottom rises. By this process, the suppression pool is mixed enough and the surface temperature of the pool is lowered, and consequently the inner pressure of the nuclear reactor pressure vessel at the LOCA can be lowered.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is directed to a loss of coolant accident (loss of coolant accident) in a boiling water nuclear reactor.
The present invention relates to the structure of an emergency core cooling system that achieves long-term cooling and maintenance of core flooding during LOCA.

[Conventional technology]

As described in Japanese Unexamined Patent Publication No. 57-69289, conventional equipment uses gravity to move coolant into the reactor by equalizing the pressure in the upper space of the pressure vessel and the pressure in the upper space of the suppression pool during LOCA. The mechanism was to inject it into a pressure vessel.

[Problem to be solved by the invention]

In conventional emergency core cooling systems, piping connects the bottom of the suppression pool and the pressure vessel, and pool water is injected into the pressure vessel by gravity during LOCA. It wasn't taken into account.

SUMMARY OF THE INVENTION An object of the present invention is to provide an emergency core cooling system capable of mitigating temperature stratification occurring in a suppression pool.

[Means to solve the problem]

In order to achieve the above objective, the emergency core cooling system has a structure in which the water intake on the suppression pool side is installed at the top of the suppression pool where the temperature is high, and the coolant return pipe is routed through the bottom of the pool where the temperature is low. It is.

[Effect]

Steam released from the pressure vessel to the dry well during LOCA is led to a lower pressure suppression chamber through a vent pipe and condensed in the suppression pool water, thereby suppressing the pressure inside the containment vessel.

Additionally, during the condensation process in the suppression pool, the heat of condensation is transferred to the pool water near the steam injection point, and is then transferred to the entire pool by natural convection.

However, during the long-term cooling process, there is almost no natural convection below the steam injection position and the temperature does not rise. On the other hand, the amount of coolant increases in the pressure suppression chamber due to condensation of steam, but the pressure in the pressure vessel and the free liquid level in the vent pipe become equal due to the opening of the automatic pressure reducing valve, and the coolant in the pressure suppression chamber flows into the pressure vessel due to gravity. Injected. The high-temperature coolant taken in from the water intake at the top of the sub-reduction pool passes through the low-temperature bottom of the suppression pool on the way to the pressure vessel through the coolant return pipe, and the heat dissipated from the high-temperature return pipe cools the bottom of the suppression pool. This increases the temperature and creates natural convection across the suppression pool. As a result, temperature stratification occurring in the suppression pool is alleviated, pool water can be used effectively, the surface temperature of the suppression pool can be lowered, and the pressure inside the containment vessel can be suppressed.

A feature of the present invention is that the emergency core cooling system, which used to inject suppression pool water into the core for long-term cooling and maintenance of core flooding, can now be suppressed by simply changing the structure in which the coolant return pipe passes through the bottom of the suppression pool. It is possible to alleviate the temperature stratification that occurs in the pool and to keep the pressure inside the containment vessel low during LOCA.

〔Example〕

FIG. 1 shows an embodiment of the invention. JIItfi. has been done.

Moreover, FIG. 2 is a detailed view of the pressure suppression chamber 3 of the same embodiment. At the time of LOCA, steam is released from the pressure vessel 1 into the dry well 2, is led to the suppression pool 4 through the vent pipe 5, and is condensed, causing the water level in the pressure suppression chamber 3 to rise. On the other hand, by opening the automatic pressure reducing valve 6, the pressures in the pressure vessel 1 and the free liquid in the vent pipe 5 become equal, and the pressure in the coolant return pipe 8 at the inlet 9 of the pressure vessel 1 and the free liquid in the vent pipe 5 becomes equal. Due to the height of the liquid level 7, an increased amount of the coolant in the pressure suppression chamber 3 is injected into the pressure vessel 1 due to gravity. On this occasion,
Since the high temperature water taken in from the water intake port 10 installed at the upper part of the suppression pool 4 passes through the low temperature bottom of the pool via the return pipe 8, the water temperature at the bottom of the pool rises due to heat radiation from the return pipe 8 to the bottom of the pool. This allows natural convection to mix the whole pool well. Note that a check valve 1l is installed in the return pipe 8, so that the coolant does not flow from the pressure vessel 1 to the pressure suppression chamber 3 side. This embodiment has the effect of lowering the surface temperature of the suppression pool 4 and keeping the pressure inside the containment vessel low.

FIG. 3 shows an embodiment in which the present invention is applied to a natural heat dissipation type containment vessel that performs a long-term cooling function of the containment vessel without using dynamic equipment. It consists of a pressure suppression chamber 3 containing a suppression pool 4 and an outer peripheral pool 12 installed on the outside of the containment vessel separated by a containment vessel wall 13. When the temperature stratification that occurs in the suppression pool 4 is alleviated by the present invention, the area of the containment vessel wall 13 that contributes to heat transfer from the suppression pool 4 to the outer circumferential pool 12 is expanded, and from the suppression pool 4 to the outer circumferential pool 2. The amount of heat transfer increases. In this embodiment, the suppression pool 4
This has the effect of increasing the amount of heat transferred from the to the outer peripheral pool 12 and keeping the pressure inside the containment vessel low.

〔Effect of the invention〕

In the present invention, the temperature at the bottom of the pool is increased by passing the coolant return pipe through which high-temperature suppression pool water passes through the bottom of the low-temperature suppression pool. As a result, natural convection occurs throughout the pool, and the entire suppression pool water is well mixed, resulting in the following effects:

(1) Compared to when the subtraction boule is not well mixed, the pool surface temperature is lower, and the pressure inside the reactor containment vessel during LOCA can be lowered.

(2) When the present invention is applied to a natural heat dissipation type containment vessel, the heat transfer area from the subrection boule to the outer pool increases, improving the heat dissipation effect.

[Brief explanation of drawings]

Fig. 1 is a vertical sectional view of a reactor containment vessel according to an embodiment of the present invention, Fig. 2 is a detailed view of the pressure suppression chamber of the same embodiment, and Fig. 3 is a detailed view of the pressure suppression chamber of the same embodiment.
The figure is a longitudinal cross-sectional view of a pressure suppression chamber and a peripheral pool of an embodiment in which the present invention is applied to a natural heat dissipation type containment vessel. 1...Reactor pressure vessel, 2...Dry well, 3.
・・Pressure suppression chamber, 4・・Suppression pool, 5・
...Vent pipe, 6...Automatic pressure reducing valve, 7...Free liquid level, 8...Coolant return pipe, 9...Inlet, 10...
Water intake, 11... Check valve, 12... Perimeter pool, 1
3...Containment vessel wall.

Claims (1)

[Claims] 1. A pressure vessel housing a nuclear reactor core, a dry well containing the pressure vessel, and a pressure suppression chamber having a coolant inside;
In this reactor containment vessel equipped with a suppression pool in a pressure suppression chamber, a coolant return pipe is provided that connects the pressure vessel and the suppression pool, and coolant from the suppression pool is supplied to the pressure vessel. Emergency core cooling system. 2. In the reactor containment vessel according to claim 1, the coolant return pipe connecting the pressure vessel and the suppression pool has a structure in which the coolant return pipe connects to the pressure vessel from the water intake in the upper part of the suppression pool via the bottom of the pool. An emergency core cooling system featuring: